A well known family of plastics comprise the so-called polyester resins prepared by esterification of a mixture of ingredients including a polyhydric alcohol and an unsaturated polycarboxylic acid, such materials being combined, typically, with cross-linking monomers typified by styrene and vinyl toluene along with various fillers, flow modifiers, thixotropic agents, flame retardant materials, plasticizers and the like. These are generally stable until mixed with an initiator or curing agent which is typically of the well known peroxide type, whereupon they cure to an infusible, solvent-resistant state. Such materials are described in detail in U.S. Pat. Nos. 3,302,410; 3,324,662, 3,324,663 and 3,731,791, the disclosures of which are incorporated herein by reference.
A uniquely important utility for such polymerizable resins is in the art of "mine roof bolting" which is described in U.S. Pat. No. 3,731,791, and elsewhere. In such use, the polymerizable resin is filled into a cartridge, and the crosslinker is also placed in the cartridge, but separated generally by mechanical means from the resin. A hole is drilled upwardly into the mine roof, one or more of the resin-crosslinker packages is inserted, and a long bolt is rammed into the hole and turned until mixing is complete. This operation breaks the resin package and mixes the resin with the crosslinker. As a result, the bolt is fastened strongly into the hole by the cured resin. What is required in this type of application is cure speed. The faster the resin cures the better. Curing at ambient temperatures, e.g., 10.degree.-30.degree. C. is accelerated in known ways, e.g., by adding to the polymerizable resin composition an accelerator, such as an amine, e.g., a tertiary amine, but this has a serious effect on the storage stability of the uncatalyzed composition.
For example, it has been found that unusually large quantities of t-amine accelerators, e.g., up to about 3% by weight, are needed to give rapid, catalyzed cure times. But these large quantities will gel the uncatalyzed resin composition in only a few days. Although U.S. Pat. No. 3,437,715 suggests that soluble copper salts in combination with quaternary ammonium salts act as inhibitors, these compositions contain only the conventional quinone type inhibitors, and no accelerators of the t-amine type. Applicants' copending application Ser. No. 7,793, filed Jan. 30, 1979, discloses the use of sodium compounds, e.g., sodium carbonate, as stabilizers, but these are not particularly adaptable to long term storage in unfilled systems.
It has now been surprisingly discovered that highly accelerated, but uncatalyzed unsaturated polyester systems can be remarkably storage stabilized by including as a stabilizer a combination of a soluble copper salt and a quaternary ammonium salt. The shelf life of packages filled with such compositions can be extended from only several days without the stabilizer to well in excess of one year with it.